Document Number: 73541

S-52083–Rev. A, 10-Oct-05

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5

Vishay Siliconix

SiP12201

New Product

Fault State:

The IC can only enter into Fault mode after the soft

start mode has ended and seven consecutive over cur-

rent condition cycles has occurred. Once it enters the

Fault state, with the High Side MOSFET turned off and

the Low Side MOSFET turned on, any occurring over

current condition will be ignored. The Fault State will

last for seven soft start cycles. After which the IC will

enter Soft Start mode. If the over current condition is

removed the IC will operate normally, otherwise the

over current sequence is repeated. This fault scheme

minimizes thermal stress on the external power MOS-

FET switches.

Over Temperature:

When the temperature of the chip goes above 165 °C,

the chip enters into over temperature shutdown. The

High Side gate will be off and the Low Side gate will be

on. Only system monitor circuitry will be active. Once

the temperature of the chip drops below 145 °C, the

chip enters into the normal operation mode.

The SiP12201 output voltage is adjustable down to 0.6

V. However, the minimum duty factor may limit the

ability to supply low-voltage outputs from high voltage

inputs. With high-input voltages, the required duty fac-

tor is approximately:

synchronous rectifier. The SiP12201 minimum duty

that can supply a given output voltage is:

If the circuit cannot attain the required duty factor dic-

tated by the input and output voltages, the output volt-

age still remains in regulation. However, there may be

intermittent or continuous half-frequency operations as

the controller attempts to lower the average duty factor

by deleting pulses. This can increase output voltage

ripple and inductor current ripple, which increases

noise and reduces efficiency. Furthermore, circuit sta-

bility is not guaranteed.

Setting the Output Voltage:

to a resistive divider between the output and GND.

Select resistor R2 in the 1 k

Ω to 10 kΩ range. R1 is

then given by:

()

IN

LOAD

DS(ON)

OUT

V

I

R

V

×

+

(

)

LOAD

DS(ON)

OUT

)

(

I

R

V

10

×

+

≤

MAX

IN

V

(

)

1

V

V

R

R

FB

OUT

2

1

−

=

R1

R2

0.6 V

FB

VOUT